Methods for cooling superconducting materials include a method in which the superconducting material is formed into a braided wire having a structure similar to that of a coaxial cable, and the coolant is sealed inside the central hollow space of the superconducting material such as that disclosed in Japanese Laid-Open Utility Model Application No. 62-66118. Conventionally, however, it has been necessary to wrap the circumference of such a superconducting material with a large amount of copper in order to maintain stable superconduction of the wire material. As a result, a vicious cycle is created in which heat is generated by the resistance arising from faults in the crystalline arrangement of the superconducting material and this heat leads to a further increase in resistance.